1. Field of the Invention
The present invention relates to a developing device provided with a developing roller for supplying a developer to a photoconductor, a supply roller for supplying the developer to the developing roller and a restricting member for restricting the amount of the developer supplied onto the supply roller and an image forming apparatus provided with this developing device.
2. Description of the Related Art
Conventionally, an image forming apparatus provided with a developing roller for supplying a toner to a photoconductor, a supply roller for supplying a developer to the developing roller and a restricting member for restricting the amount of the developer supplied onto the supply roller has been used in a color image forming apparatus like the one, for example, disclosed in Japanese Unexamined Patent Publication No. H09-274386.
A developer used for development in such an image forming apparatus tends to reduce the charging performance of carrier because toner components and fine particles adhering to the toner surfaces adhere to the carrier surfaces due to heat and stress.
However, as illustrated in FIG. 3, in the image forming apparatus disclosed in Japanese Unexamined Patent Publication No. H09-274386, a supply roller 7 includes a magnetic pole 9a for receiving a developer agitated and conveyed by a second screw 5b as being arranged to face the second screw 5b and a magnetic pole 9b for transferring the developer to a developing roller 11 as being arranged to face the developing roller 11, and a restricting blade 13 is provided as an example of a restricting member for restricting the amount of the developer to be supplied onto the developing roller 11. The supply roller 7 is rotated in a clockwise direction indicated by an arrow Y2, whereby the developer adhering around the supply roller 7 is conveyed from an area facing the second screw 5b to an area facing the developing roller 11. The developer supplied onto the developing roller 11 in the facing parts of the supply roller 7 and the developing roller 11 is blocked by the restricting blade 13 so that only a restricted fixed amount of the developer passes the restricting blade 13 to be supplied to the developing area (the area facing the photoconductor). Accordingly, the developer blocked by the restricting blade 13 stays in the vicinity of (upstream in a conveying direction of the developer indicated by an arrow Y1) the restricting blade 13 and the developer is successively supplied from the supply roller 7, wherefore the developer cannot flow anywhere.
Thus, a strong stress is applied onto the developer, which is blocked by the restricting blade 13 due to friction between the developer supplied by the rotations of the supply roller 7 and the developer, and whereby causes the following problems. That is, heat is generated in the part where the developer stays, and toner components and fine particles adhering to toner surfaces adhere to carrier surfaces. Consequently, the performances of the carriers become poorer, which in turn causes a problem of the scattering of the toner. The respective surfaces of the supply roller 7 and the developing roller 11, which face each other, move in opposite directions, and therefore, a strong stress is applied onto the developer held on the supply roller 7 due to friction when the developer passes between the supply roller 7 and the developing roller 11, which further lowers the charging performances of the carrier.